SLC.NET Presents: Steve Smith (ardalis) - Clean Architecture with ASP.NET Core

Below are the notes that I took from this online presentation with Steve Smith. This presentation was done very early into the COVID-19 pandemic. In an effort to learn more about C# and the .NET Core framework, I found that this event was happening on Meetup. So I decided to attend. You can also join The SLC .NET User Group on Meetup.

Applying Clean Architecture to ASP.NET Core

April 9, 2020

separation of concerns

  • dont let your plumbing code pollute your software
  • avoid mixing different code responsibilties in the same method, class or project

the big three

  • data access
  • business rules and domain model
  • user interface

single responsibiity

  • avoid tightly coupling your tools together
  • works in tandem with Separation of Concenrs
  • class should focus on single responsibily; should only have one reason to change

Dont Repeat Yourself (DRY)

  • put repetitive code into functions
  • group functions into cohesive classes; dealing with the same responsbility
  • group classes by folders and namespaces by responsibiltiy, level of abstraction, etc
  • further group class folders into projects

Dependency Inversion

  • Would you solder a lamp directly into the electrical wiring in a wall?

invert (and inject) dependencies

  • both high level classes and implementation-detail classes should depend on abstractions (interfaces); should not be hard coded
  • classes should follow explicit dependencies principle; classes should be explicit about all of the classes that they need; dependencies are defined in the class constructor
  • make your types honest, not deceptive
  • dont have a constructor with a lot of dependencies. consider using additional classes if this is the case
  • advised not to use property dependency injection

abstractions/inferfaces must be defined somewhere accessible by

  • low level implemetnation services
  • high level business services
  • user interface entry points; usually done in configure services

Dependency Graphs

Direct Dependency Graph

  • Class A -> Class B -> Class C

Inverted dpedency graph

  • Class A -> Inteface B -> Class B -> Interface C -> Class C
  • this allows the actual class to be swapped out and easier to test

Make the right thing easy and the wrong thing hard

  • UI classes shouldnt depend on infrastructure classes (file system, database, external resources, etc)
  • how can we strcuture our solution to help enforce this?
  • business / domain classes shouldnt depend on infrastructure classes
  • avoid repeating or copy pasting (DRY)

Class N Tier Architecture (or N Layer)

  • originally, everything was in the same layer (Classical)
  • over time, that changed to N-tier where each layer is separated

Transitive dependencies

  • this resulted in everything on the database because the top layer depended on the later below it
  • this mean that the database had to be reset each time the tests were ran

domain-centric design

  • better than data centric design

domain model

  • model of the problem that exists of entities, interfaces, services, and more
  • should be able to work independent of the database
  • interfaces define contracts for work with domain objects
  • everything in the application (including infrasctrucutre and data access) depends on these interfaces and domain objects

clean architecture (aka Onion Architecture)

  • each layer points to the inside layer
  • the domain entities at the center; they should be protected from being coupled; it makes things easier to test
  • the middle circles are what everything depends on; outer circles are other services and depend on the things in the middle

  • domain model represents the entities and abstractions; not the repository thought, just the interface

clean architecture "rules"

  • application core contains the domain model
  • all projects depends on the core project; dependencies point inward to the application core
  • inner projects define intefaces; outer projects implement them (like infrastructure)
  • abstraction lives in core; impementation lives in outter
  • avoid direct depednecy on the infrastructure project (except from integration test and possbily startup.cs); controllers should not be using things from the infrastructure
  • framework independent
  • database independent
  • UI independent
  • it is very testable
  • everything knows about core

refactoring to a clean architecture

  • best: start from properly configured project
  • next best: start from single application project
  • most difficult: large, existing investment in multilayer architecture

the core project (domain)

Minimal dependencies - none on infrastructure What goes in it

  • interfaces
  • entities, value objects, aggregates
  • domain services
  • custom exceptions
  • domain events
  • event handlers
  • specifications

infrastructure project

all dependencies on out of process resources

  • repositories
  • ef core, dbcontext
  • cached repositories
  • web api clients
  • file system
  • logging
  • email / sms sending
  • system clock
  • other services
  • interfaces (sometimes; these are for the ones that depends on infrastructure stuff)

web project

  • controllers
  • views
  • view models (or api models, or binding models)
  • filters
  • binders
  • tag / html helpers
  • other services
  • interfaces (that depend on UI stuff)

shared kernel

  • items that are shared between multiple solutions
  • referenced by the core projects
  • ideally distributed as nuget packages

solution structure - clean architecture

functional test -> web web -> infrastructure web -> core infrastructure -> core unit tests -> core integration tests -> infrastructure core -> shared kernel

how to keep controllers smaller

  • dont use a lot of logic in them; especially if it is not UI related
  • accept a type (view model, api model)
  • perform model validation
  • do work
  • create model required for response
  • return with result type (view, page, ok, not found)

do work

  • get entity from injected repository
  • work with the entity and its methods
  • update the entitys state using the repository

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